diff --git a/core/libs/prx/libSceRtc/Export.cpp b/core/libs/prx/libSceRtc/Export.cpp
index 272b78cb3..3a0895ae1 100644
--- a/core/libs/prx/libSceRtc/Export.cpp
+++ b/core/libs/prx/libSceRtc/Export.cpp
@@ -109,6 +109,7 @@ std::int64_t localOffsetSeconds(std::uint64_t utcTick) {
 
 int addTicks(RtcTick* dst, const RtcTick* src, std::int64_t count, std::int64_t unit) {
     if (!dst || !src) return SCE_RTC_ERROR_INVALID_POINTER;
+    if (src->tick > MAX_TICK) return SCE_RTC_ERROR_INVALID_VALUE;
     if (count != 0 && (count > std::numeric_limits<std::int64_t>::max() / unit || count < std::numeric_limits<std::int64_t>::min() / unit)) return SCE_RTC_ERROR_INVALID_VALUE;
     const std::int64_t delta = count * unit;
     if (delta < 0 ? src->tick < static_cast<std::uint64_t>(-(delta + 1)) + 1 : MAX_TICK - src->tick < static_cast<std::uint64_t>(delta)) return SCE_RTC_ERROR_INVALID_VALUE;
@@ -118,6 +119,7 @@ int addTicks(RtcTick* dst, const RtcTick* src, std::int64_t count, std::int64_t
 
 int addMonths(RtcTick* dst, const RtcTick* src, std::int64_t months) {
     if (!dst || !src) return SCE_RTC_ERROR_INVALID_POINTER;
+    if (src->tick > MAX_TICK) return SCE_RTC_ERROR_INVALID_VALUE;
     RtcDateTime time = fromTick(src->tick);
     const std::int64_t monthIndex = time.year * 12 + (time.month - 1) + months;
     const std::int64_t year = monthIndex / 12;
diff --git a/core/libs/tests/GuestRtc.cpp b/core/libs/tests/GuestRtc.cpp
index 23d203f06..fca1f2688 100644
--- a/core/libs/tests/GuestRtc.cpp
+++ b/core/libs/tests/GuestRtc.cpp
@@ -4,6 +4,7 @@
 #include <cstdlib>
 #include <cstring>
 #include <exception>
+#include <limits>
 
 extern "C" {
 int APS5_VABI sceRtcCheckValid(const RtcDateTime*);
@@ -168,6 +169,38 @@ int main() {
     Require(sceRtcTickAddTicks(&result, &source, 1) == invalidValue);
     Require(sceRtcTickAddTicks(nullptr, &source, 1) == invalidPointer);
 
+    const std::uint64_t invalidTicks[] = {maxTick + 1, std::numeric_limits<std::uint64_t>::max()};
+    for (std::uint64_t invalidTick : invalidTicks) {
+        source.tick = invalidTick;
+        result.tick = 123;
+        Require(sceRtcTickAddTicks(&result, &source, 0) == invalidValue && result.tick == 123);
+        Require(sceRtcTickAddTicks(&result, &source, 1) == invalidValue && result.tick == 123);
+        Require(sceRtcTickAddTicks(&result, &source, -1) == invalidValue && result.tick == 123);
+        Require(sceRtcTickAddSeconds(&result, &source, 0) == invalidValue && result.tick == 123);
+        Require(sceRtcTickAddDays(&result, &source, -1) == invalidValue && result.tick == 123);
+        Require(sceRtcTickAddMonths(&result, &source, 0) == invalidValue && result.tick == 123);
+        Require(sceRtcTickAddYears(&result, &source, -1) == invalidValue && result.tick == 123);
+        Require(sceRtcTickAddTicks(&source, &source, 0) == invalidValue && source.tick == invalidTick);
+        Require(sceRtcTickAddMonths(&source, &source, -1) == invalidValue && source.tick == invalidTick);
+        Require(sceRtcTickAddTicks(nullptr, &source, 0) == invalidPointer);
+        Require(sceRtcTickAddMonths(nullptr, &source, 0) == invalidPointer);
+    }
+
+    source.tick = maxTick;
+    Require(sceRtcTickAddTicks(&source, &source, 0) == 0 && source.tick == maxTick);
+    Require(sceRtcTickAddTicks(&source, &source, -1) == 0 && source.tick == maxTick - 1);
+    source.tick = maxTick;
+    Require(sceRtcTickAddMonths(&source, &source, 0) == 0 && source.tick == maxTick);
+    Require(sceRtcTickAddYears(&result, &source, -1) == 0);
+    Require(sceRtcSetTick(&converted, &result) == 0 && Equal(converted, RtcDateTime{9998, 12, 31, 23, 59, 59, 999999}));
+    result.tick = 123;
+    Require(sceRtcTickAddMonths(&result, &source, 1) == invalidValue && result.tick == 123);
+    Require(sceRtcTickAddTicks(&result, &source, std::numeric_limits<std::int64_t>::min()) == invalidValue && result.tick == 123);
+    Require(sceRtcTickAddSeconds(&result, &source, std::numeric_limits<std::int64_t>::max()) == invalidValue && result.tick == 123);
+    source.tick = 0;
+    Require(sceRtcTickAddMonths(&source, &source, 0) == 0 && source.tick == 0);
+    Require(sceRtcTickAddMonths(&result, &source, -1) == invalidValue && result.tick == 123);
+
     RtcTick now{};
     Require(sceRtcGetCurrentTick(&now) == 0 && now.tick > leapDayTick);
     RtcTick local{};